Hand-held valve assemblies have been used for decades to clean the inside walls of tubular members with high pressure water. The valve assembly, which is commonly referred to as a gun, may be connected to a stationary high pressure fluid source, such as a pump. Fluid is discharged from the nozzle end of the gun and, for many purposes, may be discharged at pressures at 10,000 psi or more. For applications such as cleaning heat exchanger tubes, it is desirable that the nozzle rotate with respect to upstream valve assembly components of the hand-held gun. Swivels have accordingly been used between the nozzle and the gun body to achieve nozzle rotation, thereby improving the efficiency of the cleaning operation. U.S. Pat. No. 3,987,963 discloses a high pressure gun with a swivel for rotating the nozzle with the elongate gun barrel or lance. An improved swivel having a seal cartridge and a cap with vent openings is disclosed in U.S. Pat. No. 4,690,325.
It is desirable to minimize friction in the swivel, so that rotation of the nozzle is obtained at relatively low fluid pressure, and so that the maximum possible pressure is supplied to the nozzle to perform the desired cleaning operation. On the other hand, the nature of a swivel rotatably responsive to high pressure fluid flow is such that, once the rotatable elements start rotating, their rotational speed tends to increase, thereby causing the nozzle to rotate at excessively high speeds. Accordingly, sufficient friction must be provided to maintain the desired balance which will allow the nozzle to rotate, but will not allow the nozzle to rotate at excessively high speeds.
One technique for achieving this desired balance includes the use of a magnetic rotor assembly, as disclosed in U.S. Pat. No. 5,060,862. The magnetic rotor assembly within a swivel of the high pressure gun significantly complicates the cost and the weight of the swivel. The gun operator typically is manually holding the gun body, and the swivel and nozzle are provided at the discharge end of an elongate gun barrel or lance. High swivel weight is particularly undesirable since the effective weight of the swivel is undesirable enhanced by the cantilevered lance. Prior art nozzles typically have a weight of from 50 ounces to 90 ounces, and accordingly this weight and the associated cost of a swivel with a magnetic rotor assembly significantly detract from the advantages of a high pressure gun with a rotatable nozzle.
Another problem with high pressure nozzle and swivel assemblies relates to the flow path of fluid between the inlet to the swivel and the discharge from the nozzle jets. In many guns, high pressure fluid is transmitted through a flow path which has various 90 degree bends. These turns and flow path bends not only decrease the final fluid pressure to the nozzle, but also tend to adversely affect the desired pattern of fluid discharged from the plurality of nozzle jets, thereby adversely affecting the cleaning efficiency. A desired swivel and nozzle assembly is thus able to transmit high pressure fluid at a reasonable flow rate with a minimum pressure drop across the swivel and nozzle assembly.
Swivels for high pressure fluid transmission generally can be classified as either being of the balanced system type or the in line type. A balanced system swivel balances the fluid forces axially acting on the hollow shaft which supplies fluid to the nozzles, thereby avoiding problems associated with axial thrust forces being exerted on the hollow shaft. The balanced system swivel unfortunately must have a relatively large radial design, since fluid flow between the shaft and the nozzles is generally perpendicular to the axis of the hollow shaft, i.e., fluid turns 90 degrees as it exits the shaft and flows toward the nozzles. Balanced system swivels typically experience a large amount of fluid leakage, often as much as 30 percent or more, partially because of the comparatively large sealing diameter required by this design. The relatively large radial dimension practically required for the balanced system swivel also disadvantageously increases the weight of the swivel.
An in line swivel transmits fluid in a substantially axial direction to and through the hollow shaft of the swivel. Accordingly, this type of swivel generally results in significantly less of a pressure drop than the balanced system swivel. Since the seal between the stationary bushing and the rotary shaft may have a smaller diameter than a balanced system seal, the in line swivel also generally experiences less fluid loss than a balanced system swivel. Unfortunately, the fluid pressure which axially acts upon the rotating shaft must countered, and the cost and maintenance of thrust bearings have significantly limited acceptance of this type of swivel.
Prior art swivel and nozzle assemblies typically cannot be easily disassembler and repaired. The design and configuration of the swivel and nozzle are typically complex, and the gun operator frequently cannot service the swivel and nozzle assembly at a job site. Accordingly, the gun operator tends to continue to use the gun after the time when the gun should be serviced, which causes further damage to components of the gun and also decreases the efficiency of the cleaning operation.
The disadvantages of the prior art are overcome by the present invention, and an improved swivel and nozzle assembly for a high pressure gun are hereinafter disclosed. The swivel jet assembly according to the present invention is relatively inexpensive, is light weight, results in a relatively low pressure drop and thus transmits high fluid pressure to the nozzle jets, results in a desired uniform spray pattern, and is easy to disassemble and service.